The invention is in the field of medical science and surgery, and in particular in the field of wound dressings. Foaming of combined fluid streams, including fluid streams of different viscosities, may be useful in a wide variety of settings including the medical field, the food industry, electronics, automotive, cosmetic, energy, petroleum, pharmaceutical, chemical industries, manufacturing and others. In the fuel or energy industries, inline mixing of air, water or other components with fuel may be helpful to increase engine yield, create environmentally safer or cleaner fuels.
It has been known for some time that mixtures of fibrinogen and thrombin may be applied to wounds, such as open wounds of a person, to close the wound, stop the bleeding, and prevent other substances, such as infectious agents, from entering the wound. Fibrin is a well known tissue sealant that is made from a combination of at least two primary components, fibrinogen and thrombin, which have viscosities that depend greatly on the temperature. For example, the viscosity of fibrinogen varies from about 350 cst at 15° C. to less than 100 cst at 37° C. Upon coming into contact with each other, the fibrinogen and thrombin interact to form a tissue sealant, fibrin. The quality of the fibrin generated will substantially depend on the completeness of the mixing of the two components.
Fibrinogen and thrombin are generally provided in lyophilized form and stored at very low temperatures. Lyophilized fibrinogen is typically reconstituted with sterile water before use. Thrombin is also reconstituted with sterile calcium chloride or water, such as distilled water, before use. Saline, phosphate buffered solution (PBS), or other reconstituting liquid can also be used. In preparing fibrin, the reconstituted fibrinogen and fibrin are then combined to form fibrin.
In-line mixing techniques have been discovered for mixing thrombin and fibrinogen to from a wound sealant. The sealant may be applied by a dispenser that ejects the sealant directly onto the tissue or other substrate or working surface. Examples of tissue sealant dispensers are shown in U.S. Pat. Nos. 4,631,055, 4,846,405, 5,116,315, 5,582,596, 5,665,067, 5,989,215, 6,461,361 and 6,585,696, 6,620,125 and 6,802,822 and PCT Publication No. WO 96/39212, all of which are incorporated herein by reference. Further examples of such dispensers also are sold under the Tissomat® and Duploject® trademarks, which are marketed by Baxter AG.
Typically, in these prior art devices, two individual streams of the fibrinogen and thrombin components are combined and the combined stream is dispensed to the work surface. Combining the streams of fibrinogen and thrombin initiates the reaction that results in the formation of the fibrin sealant. The liquid fibrin sealant is frequently referred to as a fibrin gel. While thorough mixing is important to fibrin formation, fouling or clogging of the dispenser tip can interfere with proper dispensing of fibrin. Clogging or fouling may result from contact or mixing of the sealant components in the dispenser and the formation of a significant quantity of viscous fibrin in the passageway prior to ejection of the components from the dispensing tip.
This clogging may result from using a high concentration of thrombin, such as 250 IU/ml. As is clear from the clogging, high concentrations of thrombin result in a much faster setting time, but may also result in incomplete mixing and binding between the thrombin and the fibrinogen, and thus an incomplete formation and release of fibrin to enable clotting. If the formulation also includes growth factor, such as platelet development growth factor (PDGF), it is believed that a high thrombin concentration causes poor binding of the growth factor to fibrin and therefore a poor release into the wound, where it would otherwise help to control clotting and tissue healing over time. Failure to clot as a result of the fibrin sealant curing too quickly may lead to further bleeding, causing additional loss of blood from the wound, and at a minimum delaying healing of the wound and possibly requiring further attention from a medical professional.
Curing too quickly thus may impede clotting and delay healing of the wound. However, the curing may also occur too slowly, such as when low concentrations of thrombin are used. If the sealing compound does not cure and become firm reasonably quickly, the sealing compound may fall away or drip from the wound. If blood or other body fluids are involved, this creates a very unsightly and potentially hazardous condition. If the compound has fallen away from the wound site, and is not present, it cannot help to seal the wound or release fibrin into the wound to encourage clotting.
One innovation to solve these problems has been to mix air with one or the other of fibrinogen or thrombin, as seen in U.S. patent application Ser. No. 11/624,113, filed Jan. 17, 2007, which is assigned to the assignee of the present patent, and which is hereby incorporated by reference. This patent application proposes mixing aqueous fibrinogen at about 100 mg/ml concentration in one container, with another container having 2.5 ml thrombin at about a 4 IU/ml concentration and 2.5 ml air. The mixing technique includes transferring the components back and forth several times, at least two times, to create a fibrin foam. This foam has a relatively higher volume of air and, of course, a low density, a low concentration of fibrinogen and thrombin per unit volume, and a resulting low concentration of fibrin per unit volume in the foam. This low concentration results in a very long setting time to create a fibrin network. The drawback is that the conventional procedure to make a fibrin glue remains a technique based on use of equal volumes of fibrinogen and thrombin. The main feature of the foam is its low density, and therefore it is important to reduce the volume of diluent used or to increase the percentage of air in the foam formulation, or both.
What is needed is a better way to formulate wound dressings that will yield a firm, adherent wound dressing while controlling clotting and tissue healing.